1. Field of the Invention
The present invention relates to a mask employed in a lithographic process, and more particularly, to an improved mask for making a semiconductor device and fabrication method thereof.
2. Background of the Related Art
FIGS. 1A through 1E illustrate a related art mask fabrication method applicable to an X-ray lithography for making a semiconductor device. As shown in FIG. 1A, on an upper and lower surface of a silicon substrate 11, a membrane film 12 formed of such material as SiN.sub.x or SiC is formed. On the upper membrane film 12, an absorber film 13 formed of a light-shielding material such as Au, W or Ta is formed. An oxide film 14 formed of SiO.sub.2 is formed on the absorber film 13.
Referring to FIG. 1B, a photoresist film 15 is coated on the oxide film 14 and patterned. As shown in FIG. 1C, using the patterned photoresist film 15 as a mask, the oxide film 14 and the absorber film 13 are sequentially etched to form the patterned oxide film 14 and absorber film 13, respectively and then the patterned photoresist film 15 is removed. The patterned absorber film 13 serves as a mask against an X-ray lithography.
As shown in FIG. 1D, the central portions of the substrate 11 and the lower membrane film 12 are removed so as to expose a lower surface of the upper membrane film 12 therethrough. Finally, as shown in FIG. 1E, on the remaining lower surface of the lower membrane film 12, a glass frame 16 is attached to complete the related art mask fabrication.
However, the mask fabrication method according to the related art requires follow-up steps after forming the membrane film 12, such as forming the absorber film 13 and removing a central portion of the substrate 11 for completing the mask fabrication. A distortion is caused by a variety of stresses inflicted on the thinly formed membrane film 12 during the follow-up steps. Further, when the absorber film 13 is etched, a stress caused by plasma tends to deteriorate the mask structure, which results in an image displacement on a wafer serving as a lithographic object when an X-ray exposure using the related art mask is performed.